Expand existing mouse colonies in San Francisco and Lubeck for the purposes of breeding stocks required for the generation of aneuploid mouse embryos. Initiate the isolation of new metacentric chromosomes and introduce these chromosomes on an inbred mouse background. Analyze the frequencies of production of various trisomies and characterize the segregation patterns of various combinations of metacentric chromosomes. Develop and implement techniques for freezing preimplantation embryos carrying individual metacentric chromosomes. Continue the mapping of human chromosome 21 loci (GARS, IfRec, SOD-1) in the mouse and carry out gene dosage studies on the relevant trisomic embryo(s). Analyze the effects of chromosomal aneuploidy in the development of the brain and other organs and tissues.